Health Inequality Gini Decomposition

The Gini coefficient is the most familiar single-number summary of inequality, and applied to a health variable it captures total, inter-individual health inequality — how unequally health is distributed across all people, regardless of their socioeconomic position. Its real analytic power comes from decomposition. Robert Lerman and Shlomo Yitzhaki's 1985 covariance formulation rewrites the Gini as twice the covariance between health and its rank divided by the mean, which makes it decomposable into the contributions of separate sources or components, each weighted by its share, its own Gini, and its Gini correlation with the overall distribution. The same machinery supports a between-versus-within-group split. As Wagstaff and van Doorslaer's review of health-inequality measurement explains, this 'pure' inequality view complements socioeconomic measures like the concentration index: the Gini asks how unequal health is, while the concentration index asks how that inequality is patterned by income or rank.